U.S. patent application number 13/145263 was filed with the patent office on 2012-06-07 for pe mib slurry polymerisation.
This patent application is currently assigned to Evonik Oxeno GmbH. Invention is credited to Anne Britt Bjaland, Stefan Buchholz, Gerhard Ellermann, Arild Follestad, Michael Grass, Morten Lundquist, Ted Pettijohn.
Application Number | 20120142882 13/145263 |
Document ID | / |
Family ID | 41820269 |
Filed Date | 2012-06-07 |
United States Patent
Application |
20120142882 |
Kind Code |
A1 |
Grass; Michael ; et
al. |
June 7, 2012 |
PE MIB SLURRY POLYMERISATION
Abstract
An alkene interpolymer is prepared by polymerizing at least one
3-substituted C.sub.4-10 alkene and at least one C.sub.2-8 alkene
in a slurry polymerization using a particulate catalyst system
containing a single site catalyst.
Inventors: |
Grass; Michael; (Haltern am
See, DE) ; Pettijohn; Ted; (Magnolia, TX) ;
Buchholz; Stefan; (Hanau, DE) ; Ellermann;
Gerhard; (Marl, DE) ; Bjaland; Anne Britt;
(Porsgrunn, NO) ; Follestad; Arild; (Stathelle,
NO) ; Lundquist; Morten; (Porsgrunn, NO) |
Assignee: |
Evonik Oxeno GmbH
Marl
DE
|
Family ID: |
41820269 |
Appl. No.: |
13/145263 |
Filed: |
January 12, 2010 |
PCT Filed: |
January 12, 2010 |
PCT NO: |
PCT/EP10/50238 |
371 Date: |
October 20, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61146938 |
Jan 23, 2009 |
|
|
|
Current U.S.
Class: |
526/348.6 |
Current CPC
Class: |
C08F 4/65925 20130101;
C08F 210/16 20130101; C08F 210/14 20130101; C08F 210/16 20130101;
C08F 2500/08 20130101; C08F 210/14 20130101; C08F 2500/12 20130101;
C08F 2/14 20130101; C08F 2500/03 20130101; C08F 210/16
20130101 |
Class at
Publication: |
526/348.6 |
International
Class: |
C08F 210/08 20060101
C08F210/08 |
Claims
1. A process for the preparation of an alkene interpolymer,
comprising: polymerizing at least one 3-substituted C.sub.4-10
alkene and at least one C.sub.2-8 alkene in a slurry polymerization
in the presence of a particulate catalyst system comprising a
single site catalyst.
2. The process as claimed in claim 1, wherein said C.sub.2-8 alkene
is ethylene or propylene.
3. The process as claimed in claim 1, wherein said 3-substituted
C.sub.4-10 alkene is a compound of formula (I) ##STR00002## wherein
R.sup.1 is a substituted or unsubstituted C.sub.1-6 alkyl group and
n is an integer between 0 and 6.
4. The process as claimed in claim 3, wherein said 3-substituted
C.sub.4-10 alkene is 3-methyl-1-butene.
5. The process as claimed in claim 1, wherein said catalyst system
comprises a metallocene.
6. The process as claimed in claim 1, wherein said catalyst system
comprises a carrier.
7. The process as claimed in claim 1, which is continuous.
8. The process as claimed in claim 1, wherein the productivity
based on a total dry weight of the catalyst system is at least 1
ton polymer per kg solid catalyst system.
9. The process as claimed in claim 1, wherein said alkene
interpolymer comprises 3-substituted C.sub.4-10 alkene comonomer in
an amount of 0.01-40 wt% based on a total weight of the
interpolymer.
10. The process as claimed in claim 1, wherein said alkene
interpolymer comprises C.sub.2-8 alkene monomer in an amount of at
least 60 wt% based on a total weight of the interpolymer.
11. The process as claimed in claim 1, wherein said alkene
interpolymer has a weight average molecular weight of 20 000 to 900
000 g/mol.
12. The process as claimed in claim 1, wherein said alkene
interpolymer has a MFR2 of 0.01-5000 g/10 min.
13. The process as claimed in claim 1, wherein said alkene
interpolymer is unimodal.
14. The process as claimed in claim 1, wherein said at least
3-substituted C.sub.4-10 alkene and said at least one C.sub.2-8
alkene are different from one another.
15. An alkene interpolymer obtained by the process as claimed in
claim 1.
16. The alkene interpolymer as claimed in claim 15, comprising:
less than 1000 ppm by weight of the particulate catalyst system or
residues therefrom.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a new, high productivity,
process for the preparation of an alkene interpolymer comprising
polymerizing at least one 3-substituted C.sub.4-10 alkene and
another C.sub.2-8 alkene in a slurry reactor using a supported
catalyst system comprising a single site catalyst. The invention
also relates to interpolymers obtainable from the process.
DISCUSSION OF THE BACKGROUND
[0003] Alkenes, such as ethylene, are often copolymerized with
comonomers in order to obtain polymers having particular
properties. Thus it is common to copolymerize ethylene with
comonomers such as 1-hexene or 1-octene in order to obtain a
polymer having, for example, decreased density relative to ethylene
homopolymer. Decreasing the density of the interpolymer generally
impacts positively on a number of its mechanical properties,
potentially making the polymer more useful in a number of end
applications. Thus comonomers are generally used to tailor the
properties of a polymer to suit its target application. There are
vast numbers of commercially available ethylene interpolymers, e.
g. comprising 1-hexene or 1-octene as comonomers.
[0004] A significant proportion of alkene polymer, e. g.
polyethylene, is produced industrially using single site catalyst
systems as the resulting polymers tend to be more homogenous
thereby rendering their composition more controllable than polymers
produced using other catalyst systems and more optimal for any
particular application. When catalyst systems comprising a single
site catalyst are used during an industrial alkene polymerization,
the single site catalyst system is continuously introduced into the
reactor system along with the appropriate monomers, whilst the
desired polymer is continuously removed. The continuous addition of
fresh catalyst system is necessary because when the desired
polyalkene is removed from the reactor system, a certain amount of
catalyst system is also removed. It is thus important to provide
additional catalyst system in order to maintain the polymerization
reaction.
[0005] A disadvantage of this manufacturing set up, however, is
that the catalyst system that is removed from the reactor with the
desired polymer is present within the polymer, closely mixed
therewith. This means that the polymer must be subjected to
purification for removal of the catalyst system, otherwise the
catalyst system, typically as partially chemically modified
catalyst system residues, will continue to remain within the
polymer material during its further treatment and its use. In other
words, the catalyst system is present in the polyalkene as an
impurity.
[0006] The presence of catalyst system residues in polymers such as
polyethylene is undesirable for a number of reasons, e. g.
[0007] they make processing, e. g. to fibers or films difficult if
the residues make particles of the same size or greater than the
fiber or film thickness
[0008] they reduce the performance of the polymer in its end use,
e. g. it can reduce the optical performance of films made using the
polymer by making visually observable inhomogeneities in the film,
often called gels, specs or fish eyes
[0009] they can render polymers unsuitable for use in applications
where the level of impurities present therein is required to be
below a certain standard, e. g. in food and/or medical
applications
[0010] they, through their content of transition metals, can act as
accelerators for polymer degradation resulting eventually in
discoloration and loss of mechanical strength.
[0011] A purification step to remove catalyst system residues from
the polymer, usually called deashing, can be carried out by
extracting and washing the polymer powder obtained from the reactor
with an alcohol (e. g. isopropanol) optionally mixed with a
hydrocarbon liquid or with water. Sometimes hydrocarbon liquids are
used for the purpose, e. g. combined with suitable metal complexing
agents such as acetylacetonate. It is clear, however, that such a
process step is complex and that processes without such a
purification step are cheaper and easier to operate than ones with
deashing.
[0012] It is thus generally desirable to try to minimize the amount
of catalyst system needed to make a given amount of polymer. This
helps eliminate the need for a deashing step to overcome the
above-mentioned problems in processing and use and also to decrease
the production cost of the polymer through reduced catalyst system
cost per ton polymer. It also minimizes any safety risks associated
with the handling of catalytic materials. Additionally the ability
to use a lesser amount of catalyst system per kg of final polymer
in some cases allow production plants to increase their production
rate without having to increase their reactor size.
[0013] There are a number of known methods that usually would
increase catalyst system productivity (i. e. ton polymer/kg
catalyst system) for a given catalyst system. These include
increasing the residence time in the reactor, increasing the
polymerization temperature, increasing the concentration of monomer
and/or the concentration of comonomer. All of these approaches,
however, suffer from serious drawbacks.
[0014] Increasing the residence time can only be done by decreasing
production rate, which is economically unfavorable, or by
increasing polymer concentration in the reactor which may easily
lead to fouling and/or lumps in the reactor and ultimately to a
long stop for cleaning. Increasing the concentration of monomer has
a negative effect on production economy by reducing the relative
conversion of monomer. Increasing the concentration of comonomer
increases the incorporation of comonomer and thus, in effect, leads
to the production of a different interpolymer to the one targeted.
Increasing the polymerization temperature from the usual operation
temperature is probably the most common strategy employed to date,
but as with increasing the residence time it can lead to reactor
fouling and/or lumps in the reactor and again to a long stop for
cleaning the reactor.
BRIEF DESCRIPTION OF DRAWINGS
[0015] FIG. 1 is a plot of activity coefficient versus polyethylene
density.
[0016] FIG. 2 is a plot of comonomer content versus polyethylene
density.
DETAILED DESCRIPTION OF THE INVENTION
[0017] In view of the above described drawbacks, there is a need
for alternative polymerization processes for the preparation of
alkene polymers and, in particular, alkene interpolymers that allow
the amount of catalyst system needed to make a given amount of
polymer to be minimized. Processes that allow the reaction to be
carried out under conventional temperature and pressure conditions
as well as in conventional reactors are especially desired.
[0018] It has now been surprisingly found that the catalytic
activity of particulate catalyst systems comprising a single site
catalyst in the slurry copolymerization of 1-alkenes such as
ethylene is significantly increased by using a 3-substituted
C.sub.4-10 alkene as comonomer rather than a conventional
non-substituted, linear C.sub.4-10 alkene. As a result, a
significantly lower amount of catalyst system can be used to
manufacture a given amount of an interpolymer comprising the
3-substituted C.sub.4-10 alkene (i.e. catalyst system productivity
is significantly increased). Advantageously the major properties of
a 1-alkene/3-substituted C.sub.4-10 alkene interpolymer (e. g.
MFR.sub.2, density, melting point, Mw, Mn and molecular weight
distribution) may be maintained on a comparable level to the
properties of the conventional 1-alkene/non-substituted, linear
C.sub.4-10 alkene interpolymer. Surprisingly comparable properties
can be achieved in some cases by using less 3-substituted
C.sub.4-10 alkene as comonomer rather than a conventional
non-substituted, linear C.sub.4-10 alkene comonomer. Thus, the
process herein described offers an economically attractive approach
for making interpolymers that can be used as substitutes for the
ethylene/l-hexene and ethylene/1-octene copolymers commercially
available.
[0019] Copolymers comprising ethylene and 3-methyl-but-1-ene have
previously been described in the background art, e. g. in
WO2008/006636, EP-A-1197501 and WO2008/003020. None of these
documents, however, disclose the copolymerization of C.sub.2-8
alkene and 3-methyl-but-1-ene with a particulate catalyst system
comprising a single site catalyst. Accordingly, none of these
documents disclose or suggest that the catalytic productivity of
such a catalyst system in the slurry copolymerization of C.sub.2-8
alkene such as ethylene may be significantly increased by utilizing
3-methyl-but-1-ene as comonomer, rather than conventional
comonomers such as 1-hexene or 1-octene.
[0020] In a first embodiment, the present invention provides a
process for the preparation of an alkene interpolymer comprising
polymerizing at least one 3-substituted C.sub.4-10 alkene and
another C.sub.2-8 alkene in a slurry polymerization using a
particulate catalyst system comprising a single site catalyst.
[0021] In a second embodiment, the invention provides an alkene
interpolymer obtainable using a process as described in this patent
application.
[0022] In a third embodiment, the invention provides a method of
increasing the productivity of a particulate catalyst system
comprising a single site catalyst in a slurry polymerization
comprising polymerizing at least one 3-substituted C.sub.4-10
alkene with another C.sub.2-8 alkene.
[0023] In a fourth embodiment, the invention provides the use of a
3-substituted C.sub.4-10 alkene and a particulate catalyst system
comprising a single site catalyst in the preparation of a C.sub.2-8
alkene interpolymer by slurry polymerization.
[0024] Definitions
[0025] All ranges mentioned herein include all values and subvalues
between the lower limit and the higher limit of the range,
including the end points of the range.
[0026] As used herein, the term "alkene interpolymer" refers to
polymers comprising repeat units deriving from at least one
3-substituted C.sub.4-10 alkene monomer and at least one other
C.sub.2-8 alkene. Preferred interpolymers are binary (i. e.
preferred interpolymers are copolymers) and comprise repeat units
deriving from one type of 3-substituted C.sub.4-10 alkene comonomer
and one other type of C.sub.2-8 alkene monomer. Other preferred
interpolymers are ternary, e. g. they comprise repeat units
deriving from one type of 3-substituted C.sub.4-10 alkene comonomer
and two types of C.sub.2-8 alkene monomer. Particularly preferred
interpolymers are copolymers. In preferred interpolymers at least
0.01% wt, still more preferably at least 0.1% wt, e. g. at least
0.5% wt of each monomer is present based on the total weight of the
interpolymer.
[0027] In contrast, the term "alkene homopolymer" as used herein
refers to polymers which consist essentially of repeat units
deriving from one type of C.sub.2-8 alkene, e. g. ethylene.
Homopolymers may, for example, comprise at least 99.9% wt e. g. at
least 99.99% wt of repeat units deriving from one type of C.sub.2-8
alkene based on the total weight of the polymer.
[0028] As used herein, the term 3-substituted C.sub.4-10 alkene
refers to an alkene having: (i) a backbone containing 4 to 10
carbon atoms, wherein the backbone is the longest carbon chain in
the molecule that contains an alkene double bond, and (ii) a
substituent (i. e. a group other than H) at the 3 position.
[0029] As used herein, the term "slurry polymerization" refers to a
polymerization wherein the polymer forms as a solid in a liquid.
The liquid may be a monomer of the polymer. In the latter case the
polymerization is sometimes referred to as a bulk polymerization.
The term slurry polymerization encompasses what is sometimes
referred to in the art as supercritical polymerization, i. e. a
polymerization wherein the polymer is a solid suspended in a fluid
that is relatively close to its critical point, or if the fluid is
a mixture, its pseudocritical point. A fluid may be considered
relatively close to its critical point if its compressibility
factor is less than double its critical compressibility factor or,
in the case of a mixture, its pseudocritical compressibility
factor.
[0030] As used herein, the term catalyst system refers to the total
active entity that catalyses the polymerization reaction.
Typically, the catalyst system is a coordination catalyst system
comprising a transition metal compound (the active site precursor)
and an activator (sometimes referred to as a cocatalyst) that is
able to activate the transition metal compound. The catalyst system
of the present invention preferably comprises an activator, at
least one transition metal active site precursor and a particle
building material that may be the activator or another material.
Preferably, the particle building material is a carrier.
[0031] As used herein, the term "multisite catalyst system" refers
to a catalyst system comprising at least two different active sites
deriving from at least two chemically different active site
precursors. A multisite catalyst system used in the present
invention comprises at least one single site catalyst. Examples of
a multisite catalyst system are one comprising two or three
different metallocene active sites precursors or one comprising a
Ziegler Natta active site and a metallocene active site. If there
are only two active sites in the catalyst system, it can be called
a dual site catalyst system. Particulate multisite catalyst systems
may contain its different active sites in a single type of catalyst
particle. Alternatively, each type of active site may each be
contained in separate particles. If all the active sites of one
type are contained in separate particles of one type, each type of
particles may enter the reactor through its own inlet.
[0032] As used herein, the term "single site catalyst" refers to a
catalyst having one type of active catalytic site. An example of a
single site catalyst is a metallocene-containing catalyst. A
typical Ziegler Natta (ZN) catalyst made from, e. g. impregnation
of TiCl.sub.4 into a carrier material, or chromium oxide (Philips)
catalyst made from, e. g. impregnation of chromium oxide into
silica, are not single site catalysts as they contain a mixture of
different types of sites that give rise to polymer chains of
different composition.
[0033] As used herein, the term "particulate catalyst system" means
a catalyst system that when fed to the polymerization reactor or
into the polymerization section, has its active sites or active
site(s) precursors within solid particles, preferably porous
particles. This is, in contrast, to catalyst systems with active
sites, or precursor compounds, that are liquid or are dissolved in
a liquid. It is generally presumed that when carrying out a
polymerization using a particulate catalyst the particles of the
catalyst will be broken down to catalyst fragments. These fragments
are thereafter present within polymer particles whenever the
polymerization is carried out in conditions whereby solid polymer
forms. The particulate catalyst system may be prepolymerized during
the catalyst preparation production process or later. The term
particulate catalyst system also includes the situation wherein an
active site or active site precursor compound contacts a carrier
just before, or at the same time, as the active site or active site
precursor compound contacts the monomer in the polymerization
reactor.
[0034] As used herein, the term "polymerization section" refers to
all of the polymerization reactors present in a multistage
polymerization. The term also encompasses any prepolymerization
reactors that are used.
[0035] As used herein, the term "multimodal" refers to a polymer
comprising at least two components, which have been produced under
different polymerization conditions and/or by using a multisite
catalyst system in one stage and/or by using two or more different
catalysts in a polymerization stage resulting in different (weight
average) molecular weights and molecular weight distributions for
the components. The prefix "multi" refers to the number of
different components present in the polymer. Thus, for example, a
polymer consisting of two components only is called "bimodal". The
form of the molecular weight distribution curve, i. e. the
appearance of the graph of the polymer weight fraction as a
function of its molecular weight, of a multimodal polyalkene will
show two or more maxima or at least be distinctly broadened in
comparison with the curves for the individual components. In
addition, multimodality may show as a difference in melting or
crystallization temperature of components.
[0036] In contrast, a polymer comprising one component produced
under constant polymerization conditions is referred to herein as
unimodal.
[0037] C.sub.2-8 Alkene
[0038] In order to produce an interpolymer the C.sub.2-8 alkene
should be a different alkene to the alkene used as the
3-substituted C.sub.4-10 alkene. One or more (e. g. two or three)
C.sub.2-8 alkenes may be used. Preferably, however, one or two, e.
g. one, C.sub.2-8 alkene is used.
[0039] Preferably, the C.sub.2-8 alkene is a monoalkene. Still more
preferably the C.sub.2-8 alkene is a terminal alkene. In other
words, the C.sub.2-8 alkene is preferably unsaturated at carbon
numbers 1 and 2. Preferred C.sub.2-8 alkene are thus C.sub.2-8
alk-1-enes.
[0040] The C.sub.2-8 alkene is preferably a linear alkene. Still
more preferably, the C.sub.2-8 alkene is an unsubstituted C.sub.2-8
alkene.
[0041] Representative examples of C.sub.2-8 alkenes that are
suitable for use in the process of the present invention include
ethylene, propylene, 1-butene, 1-pentene, 4-methyl-1-pentene,
1-hexene and 1-octene. Preferably, the C.sub.2-8 alkene is selected
from ethylene, propylene, 1-butene, 4-methyl-1-pentene or mixtures
therefore. Particularly preferably, the C.sub.2-8 alkene is
ethylene or propylene, e.g. ethylene.
[0042] C.sub.2-8 alkenes for use in the present invention are
commercially available. Alternatively, ethylene, propylene and
but-1-ene may be prepared by thermal cracking. Higher linear
olefins are available from catalytic oligomerization of ethylene or
by Fischer Tropsch synthesis.
[0043] Substituted C.sub.4-10 Alkene
[0044] It has been found that the slurry copolymerization of the
above-described C.sub.2-8 alkene with 3-substituted C.sub.4-10
alkene with a particulate, single site catalyst system occurs with
unexpectedly high efficiency. It has also been found that to
provide a polymer of any given density, less 3-substituted
C.sub.4-10 alkene needs to be included therein than 1-hexene or
1-octene. This is advantageous as the cost of comonomers such as
1-hexene, 1-octene or 3-substituted C.sub.4-10 alkene is much
greater than the cost of ethylene or propylene.
[0045] Preferably, the substituent present at carbon 3 of the
3-substituted C.sub.4-10 alkene is a C.sub.1-6 alkyl group. The
alkyl group may be substituted by non-hydrocarbyl substituents or
unsubstituted. Representative examples of non-hydrocarbyl
substituents that may be present on the alkyl group include F and
Cl. Preferably, however, the C.sub.1-6 alkyl group is
unsubstituted. Particularly preferably, the substituent group
present at carbon 3 is a C.sub.1-3 alkyl group such as methyl,
ethyl or iso-propyl. Methyl is an especially preferred substituent
group.
[0046] Preferably, the 3-substituted C.sub.4-10 alkene is solely
substituted at carbon 3. If, however, a substituent is present at
another position it is preferably a C.sub.1-6 alkyl group as
described above for the substituent present at carbon 3.
[0047] The 3-substituted C.sub.4-10 alkene is preferably a
monoalkene. Still more preferably, the 3-substituted C.sub.4-10
alkene is a terminal alkene. In other words, the 3-substituted
C.sub.4-10 alkene is preferably unsaturated at carbon numbers 1 and
2. Preferred 3-substituted C.sub.4-10 alkenes are thus
3-substituted C.sub.4-10 alk-1-enes.
[0048] Preferred 3-substituted C.sub.4-10 alkenes for use in the
process of the present invention are those of formula (I):
##STR00001##
wherein R.sup.1 is a substituted or unsubstituted, preferably
unsubstituted, C.sub.1-6 alkyl group and n is an integer between 0
and 6.
[0049] In preferred compounds of formula (I) R.sup.1 is methyl or
ethyl, e. g. methyl. In further preferred compounds of formula (I)
n is 0, 1 or 2, still more preferably 0 or 1, e. g. 0.
[0050] Representative examples of compounds of formula (I) that can
be used in the process of the present invention include
3-methyl-1-butene, 3-methyl-1-pentene, 3-methyl-1-hexene,
3-ethyl-1-pentene and 3-ethyl-1-hexene. A particularly preferred
3-substituted C.sub.4-10 alkene for use in the process of the
present invention is 3-methyl-1-butene.
[0051] 3-substituted C.sub.4-10 alkenes for use in the invention
are commercially available, e. g from Sigma-Aldrich.
3-methyl-1-butene can be made, e. g. according to
WO2008/006633.
[0052] Catalyst System
[0053] As described above, it has been surprisingly found that the
copolymerization of a 3-substituted C.sub.4-10 alkene, e. g.
3-methyl-1-butene, with a C.sub.2-8 alkene, e. g. ethylene, occurs
with higher efficiency than the corresponding copolymerization with
conventional linear C.sub.4-10 alkenes. This effect has
specifically been observed with particulate catalyst systems
comprising a single site catalyst.
[0054] Catalyst Morphology and Carrier
[0055] The catalyst system used in the process of the present
invention is in particulate form. Preferably, the catalyst system
is in the form of particles having a weight average particle size
of 1 to 250 microns, preferably 4 to 150 microns. Preferably, the
catalyst system is in the form of a free-flowing powder.
[0056] The catalyst system used in the process of the present
invention comprises a single site catalyst, preferably a
metallocene-containing catalyst. Such catalyst systems are well
known in the art, e. g. from WO98/02246, the contents of which are
hereby incorporated herein by reference. The catalyst system
particles may be synthesized by producing the solid particles from
liquid starting material components without a separate impregnation
step or they may be made by first producing a solid particle and
then impregnating the active site precursors into it.
[0057] The catalyst system preferably comprises a carrier, an
activator and at least one transition metal active site precursor
(e. g. a metallocene). The activator is preferably aluminoxane,
borane or borate but preferably is aluminoxane. Preferably, the
active site precursor is a metallocene.
[0058] Suitable carrier materials for use in the catalyst system
are well known in the art. The carrier material is preferably an
inorganic material, e. g. an oxide of silicon and/or of aluminium
or MgCl.sub.2. Preferably, the carrier is an oxide of silicon
and/or aluminium. Still more preferably the carrier is silica.
[0059] Preferably, the carrier particles have an average particle
size of 1 to 500 microns, preferably 3 to 250 microns, e. g. 10 to
150 microns. Particles of appropriate size can be obtained by
sieving to eliminate oversized particles. Sieving can be carried
out before, during or after the preparation of the catalyst system.
Preferably, the particles are spherical. The surface area of the
carrier is preferably in the range 5 to 1200 m.sup.2/g, more
preferably 50 to 600 m.sup.2/g. The pore volume of the carrier is
preferably in the range 0.1 to 5 cm.sup.3/g, preferably 0.5-3.5
cm.sup.3/g.
[0060] Preferably, the carrier is dehydrated prior to use.
Particularly preferably the carrier is heated at 100 to 800.degree.
C., more preferably 150 to 700.degree. C., e. g. at about
250.degree. C. prior to use. Preferably, dehydration is carried out
for 0.5-12 hours.
[0061] Carriers that are suitable for the preparation of the
catalyst systems herein described are commercially available, e. g.
from Grace and PQ Corporation.
[0062] Activator
[0063] Aluminoxane is preferably present in the catalyst system as
activator. The aluminoxane is preferably oligomeric. Still more
preferably the aluminoxane is a cage-like (e. g. multicyclic)
molecule, e. g. with an approximate formula
(AlR.sub.1.4O.sub.0.8).sub.n where n is 10-60 and R is an alkyl
group, e. g. a C.sub.1-20 alkyl group. In preferred aluminoxanes R
is a C.sub.1-8 alkyl group, e. g. methyl. Methylaluminoxane (MAO)
is a mixture of oligomers with a distribution of molecular weights,
preferably with an average molecular weight of 700 to 1500. MAO is
a preferred aluminoxane for use in the catalyst system.
[0064] The aluminoxane may be modified with an aluminium alkyl or
aluminium alkoxy compound. Especially preferred modifying compounds
are aluminium alkyls, in particular, aluminium trialkyls such as
trimethyl aluminium, triethyl aluminium and tri isobutyl aluminium.
Trimethyl aluminium is particularly preferred.
[0065] Aluminoxanes, such as MAO, that are suitable for the
preparation of the catalyst systems herein described are
commercially available, e. g. from Albemarle and Chemtura.
[0066] It is also possible to generate the activator in situ, e. g.
by slow hydrolysis of trimethylaluminium inside the pores of a
carrier. This process is well known in the art.
[0067] Alternatively, activators based on boron may be used.
Preferred boron based activators are those wherein the boron is
attached to at least 3 fluorinated phenyl rings as described in EP
520732.
[0068] Alternatively, an activating, solid surface as described in
U.S. Pat. No. 7,312,283 may be used as a carrier. These are solid,
particulate inorganic oxides of high porosity which exhibit Lewis
acid or Bronsted acidic behavior and which have been treated with
an electron-withdrawing component, typically an anion, and which
have then been calcined.
[0069] Transition Metal Active Site Precursor
[0070] Generally, the metal of the transition metal precursors are
16-electron complexes, although they may sometimes comprise fewer
electrons, e. g. complexes of Ti, Zr or Hf.
[0071] The active site transition metal precursor is preferably a
metallocene.
[0072] The metallocene preferably comprises a metal coordinated by
one or more .eta.-bonding ligands. The metal is preferably Zr, Hf
or Ti, especially Zr or Hf The n-bonding ligand is preferably a
.eta..sup.5-cyclic ligand, i.e. a homo or heterocyclic
cyclopentadienyl group optionally with fused or pendant
substituents.
[0073] The metallocene preferably has the formula:
(Cp).sub.mL.sub.nMX.sub.p
wherein Cp is an unsubstituted or substituted cyclopentadienyl
group, an unsubstituted or substituted indenyl or an unsubstituted
or substituted fluorenyl (e. g. an unsubstituted or substituted
cyclopentadienyl group);
[0074] the optional one or more substituent(s) being independently
selected from halogen (e. g. Cl, F, Br, I), hydrocarbyl (e. g.
C.sub.1-20 alkyl, C.sub.2-20 alkenyl, C.sub.2-20 alkynyl,
C.sub.6-20 aryl or C.sub.6-20 arylalkyl), C.sub.3-12 cycloalkyl
which contains 1, 2, 3 or 4 heteroatom(s) in the ring moiety,
C.sub.6-20 heteroaryl, C.sub.1-20 haloalkyl, --SiR''.sub.3,
--OSiR''.sub.3, --SR'', --PR''.sub.2 or --NR''.sub.2,
[0075] each R'' is independently a H or hydrocarbyl, e. g.
C.sub.1-20 alkyl, C.sub.2-20 alkenyl, C.sub.2-20 alkynyl,
C.sub.6-20 aryl or C.sub.6-20 arylalkyl; or in the case of
--NR''.sub.2, the two R'' can form a ring, e. g. a 5 or 6 membered
ring, together with the nitrogen atom to which they are
attached;
[0076] L is a bridge of 1-7 atoms, e. g. a bridge of 1-4 C atoms
and 0-4 heteroatoms, wherein the heteroatom(s) can be, e. g. Si, Ge
and/or O atom(s), wherein each of the bridge atoms may
independently bear substituents (e. g. C.sub.1-20 alkyl,
tri(C.sub.1-20 alkyl)silyl, tri(C.sub.1-20alkyl)siloxy or
C.sub.6-20 aryl substituents); or a bridge of 1-3, e. g. one or
two, heteroatoms, such as Si, Ge and/or O atom(s), e. g.
--SiR.sup.'''.sub.2, wherein each R.sup.''' is independently
C.sub.1-20 alkyl, C.sub.6-20 aryl or tri(C.sub.1-20alkyl)silyl
residue such as trimethylsilyl;
[0077] M is a transition metal of Group 3 to 10, preferably of
Group 4 to 6, such as Group 4, e. g. titanium, zirconium or
hafnium, preferably hafnium,
[0078] each X is independently a sigma ligand such as halogen (e.
g. Cl, F, Br, I), hydrogen, C.sub.1-20 alkyl, C.sub.1-20 alkoxy,
C.sub.2-20 alkenyl, C.sub.2-20 alkynyl, C.sub.3-12 cycloalkyl,
C.sub.6-20 aryl, C.sub.6-20 aryloxy, C.sub.7-20 arylalkyl,
C.sub.7-20 arylalkenyl, --SR'', --PR''.sub.3, --SiR''.sub.3,
--OSiR''.sub.3, --NR''.sub.2, or CH.sub.2--Y wherein Y is
C.sub.6-20 aryl, C.sub.6-20 heteroaryl, C.sub.1-20 alkoxy,
C.sub.6-20 aryloxy, --NR''.sub.2, --SR'', --PR''.sub.3,
--SiR''.sub.3 or --OSiR''.sub.3; alternatively, two X ligands are
bridged to provide a bidentate ligand on the metal, e. g.
1,3-pentadiene;
[0079] each of the above mentioned ring moieties alone or as part
of another moiety as the substituent for Cp, X, R'' or R.sup.'''
can be further substituted, e. g. with C.sub.1-20 alkyl which may
contain Si and/or O atom(s);
[0080] m is 1, 2 or 3, preferably 1 or 2, more preferably 2;
[0081] n is 0, 1 or 2, preferably 0 or 1;
[0082] p is 1, 2 or 3 (e. g. 2 or 3); and
[0083] the sum of m+p is equal to the valence of M (e. g. when M is
Zr, Hf or Ti, the sum of m+ p should be 4).
[0084] Preferably, Cp is a cyclopentadienyl group, especially a
substituted cyclopentadienyl group. Preferred substituents on Cp
groups, including cyclopentadienyl, are C.sub.1-20 alkyl.
Preferably, the cyclopentadienyl group is substituted with a
straight chain C.sub.1-6 alkyl group, e. g. n-butyl.
[0085] If present L is preferably a methylene, ethylene or silyl
bridge whereby the silyl can be substituted as defined above, e. g.
a (dimethyl)Si.dbd., (methylphenyl)Si.dbd. or
(trimethylsilylmethyl)Si.dbd.; n is 1; m is 2 and p is 2. When L is
a silyl bridge, R'' is preferably other than H. More preferably,
however, n is 0.
[0086] X is preferably H, halogen, C.sub.1-20 alkyl or C.sub.6-20
aryl. When X are halogen atoms, they are preferably selected from
fluorine, chlorine, bromine and iodine. Most preferably, X is
chlorine. When X is a C.sub.1-20 alkyl group, it is preferably a
straight chain or branched C.sub.1-8 alkyl group, e. g. a methyl,
ethyl, n-propyl, n-hexyl or n-octyl group. When X is an C.sub.6-20
aryl group, it is preferably phenyl or benzyl. In preferred
metallocenes X is a halogen, e. g. chlorine.
[0087] Suitable metallocene compounds include:
[0088] bis(cyclopentadienyl)metal dihalides,
bis(cyclopentadienyl)metal hydridohalides,
bis(cyclopentadienyl)metal monoalkyl monohalides,
bis(cyclopentadienyl)metal dialkyls and bis(indenyl)metal dihalides
wherein the metal is zirconium or hafnium, preferably hafnium,
halide groups are preferably chlorine and alkyl groups are
preferably C.sub.1-6 alkyl.
[0089] Representative examples of metallocenes include:
[0090] bis(cyclopentadienyl)ZrCl.sub.2,
bis(cyclopentadienyl)HfCl.sub.2, bis(cyclopentadienyl)ZrMe.sub.2,
bis(cyclopentadienyl)HfMe.sub.2, bis(cyclopentadienyl)Zr(H)Cl,
bis(cyclopentadienyl)Hf(H)Cl,
bis(n-butylcyclopentadienyl)ZrCl.sub.2,
bis(n-butylcyclopentadienyl)HfCl.sub.2,
bis(n-butylcyclopentadienyl)ZrMe.sub.2,
bis(n-butylcyclopentadienyl)HfMe.sub.2,
bis(n-butylcyclopentadienyl)Zr(H)Cl,
bis(n-butylcyclopentadienyl)Hf(H)Cl,
bis(pentamethylcyclopentadienyl)ZrCl.sub.2,
bis(pentamethylcyclopentadienyl)HfCl.sub.2,
bis-(1,3-dimethylcyclopentadienyl)ZrCl.sub.2,
bis(4,5,6,7-tetrahydro-1-indenyl)ZrCl.sub.2 and
ethylene-[bis(4,5,6,7-tetrahydro-1-indenyl)ZrCl.sub.2.
[0091] Alternatively, the metallocene may be a constrained geometry
catalyst (CGC). These comprise a transition metal, M (preferably
Ti) with one eta-cyclopentadienyl ligand and two X groups, i. e. be
of the formula CpMX.sub.2, wherein X is as defined above and the
cyclopentadienyl has a --Si(R'').sub.2N(R'')-- substituent wherein
R'' is as defined above and the N atom is bonded directly to M.
Preferably, R'' is C.sub.1-20 alkyl. Preferably, the
cyclopentadienyl ligand is additionally substituted with 1 to 4,
preferably 4, C.sub.1-20 alkyl groups. Examples of metallocenes of
this type are described in US 2003/0022998, the contents of which
are hereby incorporated by reference.
[0092] The preparation of metallocenes can be carried out according
to, or analogously to, the methods known from the literature and is
within the skills of a polymer chemist.
[0093] Other types of single site precursor compounds are described
in: G. J. P. Britovsek et al.: The Search for New-Generation Olefin
Polymerization Catalysts: Life beyond Metallocenes, Angew. Chemie
Int. Ed., 38 (1999), p. 428.
[0094] H. Makio et al.: FI Catalysts: A New Family of High
Performance Catalysts for Olefin Polymerization, Advanced Synthesis
and Catalysis, 344 (2002), p. 477. Dupont-Brookhart type active
site precursors are disclosed in U.S. Pat. No. 5,880,241.
[0095] Catalyst System Preparation
[0096] To form the catalyst systems for use in the present
invention, the carrier, e. g. silica, is preferably dehydrated (e.
g. by heating). The further preparation of the catalyst system is
preferably undertaken under anhydrous conditions and in the absence
of oxygen and water. The dehydrated carrier is then preferably
added to a liquid medium to form a slurry. The liquid medium is
preferably a hydrocarbon comprising 5 to 20 carbon atoms, e. g.
pentane, isopentane, hexane, isohexane, heptane, octane, nonane,
decane, dodecane, cyclopentane, cyclohexane, cycloheptane, toluene
and mixtures thereof. Isomers of any of the afore-mentioned
hydrocarbons may also be used. The volume of the liquid medium is
preferably sufficient to fill the pores of the carrier, and more
preferably to form a slurry of the carrier particles. Typically the
volume of the liquid medium will be 2 to 15 times the pore volume
of the support as measured by nitrogen adsorption method (BET
method). This helps to ensure that a uniform distribution of metals
on the surface and pores of the carrier is achieved.
[0097] In a separate vessel, the metallocene may be mixed with
aluminoxane in a solvent. The solvent may be a hydrocarbon
comprising 5 to 20 carbon atoms, e. g. toluene, xylene,
cyclopentane, cyclohexane, cycloheptane, pentane, isopentane,
hexane, isohexane, heptane, octane or mixtures thereof. Preferably,
toluene is used. Preferably, the metallocene is simply added to the
toluene solution in which the aluminoxane is present in its
commercially available form. The volume of the solvent is
preferably about equal to or less than the pore volume of the
carrier. The resulting mixture is then mixed with the carrier,
preferably at a temperature in the range 0 to 60.degree. C.
Impregnation of the metallocene and aluminoxane into the carrier is
preferably achieved using agitation. Agitation is preferably
carried out for 15 minutes to 12 hours. Alternatively, the carrier
may be impregnated with aluminoxane first, followed by metallocene.
Simultaneous impregnation with aluminoxane and metallocene is,
however, preferred.
[0098] The solvent and/or liquid medium are typically removed by
filtering and/or decanting and/or evaporation, preferably by
evaporation only. Optionally, the impregnated particles are washed
with a hydrocarbon solvent to remove extractable metallocene and/or
aluminoxane. Removal of the solvent and liquid medium from the
pores of the carrier material is preferably achieved by heating
and/or purging with an inert gas. Removal of the solvent and liquid
medium is preferably carried out under vacuum. Preferably, the
temperature of any heating step is below 80.degree. C., e. g.
heating may be carried out at 40-70.degree. C. Typically heating
may be carried out for 2 to 24 hours. Alternatively, the catalyst
system particles may remain in a slurry form and used as such when
fed to the polymerization reactor, however, this is not
preferred.
[0099] The metallocene and aluminoxane loading on the carrier is
such that the amount of aluminoxane (dry), on the carrier ranges
from 10 to 90% wt, preferably from 15 to 50% wt, still more
preferably from 20 to 40% wt based on the total weight of dry solid
catalyst. The amount of transition metal on the carrier is
preferably 0.005-0.2 mmol/g of dry solid catalyst, still more
preferably 0.01-0.1 mmol/g of dry solid catalyst.
[0100] The molar ratio of Al:transition metal in the solid catalyst
system may range from 25 to 10,000, usually within the range of
from 50 to 980 but preferably from 70 to 500 and most preferably
from 100 to 350.
[0101] Particulate catalyst system can also be made using a boron
activator instead of aluminoxane activator, e. g. as described in
U.S. Pat. No. 6,787,608. In its example 1, an inorganic carrier is
dehydrated, then surface modified by alkylaluminum impregnation,
washed to remove excess alkylaluminum and dried. Subsequently the
carrier is impregnated with an about equimolar solution of boron
activator and trialkylaluminum, then mixed with a metallocene
precursor, specifically a CGC metallocene, then filtered, washed
and dried.
[0102] Also U.S. Pat. No. 6,350,829 describes the use of boron
activator, but using mainly bis metallocene complexes as active
site precursors. The dried metal alkyl-treated carrier is
co-impregnated with a mixture of the metallocene and the boron
activator (without additional metal alkyl), and then the volatiles
removed.
[0103] The support material may also be mixed with the metallocene
solution just before polymerization. U.S. Pat. No. 7,312,283
describes such a process. A porous metal oxide particulate material
is impregnated with ammonium sulphate dissolved in water, and then
calcined in dry air, kept under nitrogen, then mixed with a
hydrocarbon liquid. Separately a solution was prepared by mixing
metallocene with 1-alkene, and then mixing in metal alkyl.
Polymerization was done in a continuous slurry reactor, into which
both the sulphated particulate metal oxide and the metallocene
solution were fed continuously, in such a way that the two feed
streams were mixed immediately before entering the reactor. Thus
the treated metal oxide functions both as an activator as well as a
catalyst support.
[0104] Alternative methods of supporting single site catalysts via
a preformed carrier and aluminoxane are given in EP 279 863, WO
93/23 439, EP 793 678, WO 96/00 245, WO 97/29 134
[0105] Alternative methods of supporting single site catalysts via
preformed carriers and boron activators are given in WO 91/09 882
and WO 97/31 038.
[0106] Methods of obtaining particulate catalyst systems without
employing preformed carriers are given in EP 810 344 and EP 792
297.
[0107] Multisite Catalyst Systems
[0108] Multisite catalyst systems for use in the polymerization
comprise a single site catalyst.
[0109] The multisite catalyst system may be hybrids from two (or
more) different catalyst families. For instance, Ziegler Natta and
single site catalytic sites may be used together, e. g. by
impregnating metallocene site precursor and activator for the
metallocene into the pores of a particulate Ziegler Natta catalyst.
Alternatively, chromium oxide may be used together with a
metallocene, e. g. by impregnating, under inert conditions,
metallocene site precursor and activator for the metallocene into
the pores of a particulate, thermally activated chromium oxide
catalyst.
[0110] Single site catalysts are particularly useful in the
preparation of multisite catalyst systems. A preferred multisite
catalyst system is one comprising two metallocenes, e. g. one
having a tendency to make higher molecular weight polymer and one
having a tendency to make lower molecular weight polymer or one
having a tendency to incorporate comonomer and one having a lesser
tendency to do so. The two metallocenes may, for instance, be
isomeric metallocenes in about the same ratio as made in their
synthesis. Preferably, however, the multisite catalyst system
comprises one active site making a polymer component of both lower
molecular weight and lower comonomer incorporation than another
site. Dual site catalyst systems (multisite catalyst systems with
two sites) containing such sites are particularly preferred.
[0111] High Catalyst Activity/Productivity
[0112] An important feature of the process of the present invention
is that the above-described catalyst system has a high activity
coefficient in the copolymerization of C.sub.2-8 alkene and
3-substituted C.sub.4-10 alkene at a polymerization temperature of
about 80.degree. C. Preferably, the activity coefficient of the
catalyst system is at least 160 g polyalkene/(g cat, h, bar), still
more preferably the activity coefficient of the catalyst system is
at least 180 g polyalkene/(g cat, h, bar), e. g. at least 200 g
polyalkene/(g cat, h, bar). There is no upper limit on the activity
coefficient, e. g. it may be as high as 5000 g polyalkene/(g cat,
h, bar).
[0113] The high catalytic productivity of the process of the
present invention has many advantages. For instance, it decreases
the production cost of the polymer and minimizes any safety risks
associated with the handling of catalytic materials as less are
required. Additionally the ability to use a lesser amount of
catalyst system per kg of final polymer in most cases allows
production plants to increase their production output without
having to increase their reactor size or catalyst materials feed
systems.
[0114] Polymerization and Downstream Process
[0115] Polymerization Processes
[0116] The slurry polymerization reaction is preferably carried out
in conventional circulating loop or stirred tank reactors. Suitable
polyalkene processes are, for example, Hostalen staged (where
catalyst system and polymer sequentially pass from reactor to
reactor) tank slurry reactor process for polyethylene by
LyondellBasell, LyondellBasell-Maruzen staged tank slurry reactor
process for polyethylene, Mitsui staged tank slurry reactor process
for polyethylene by Mitsui, CPC single loop slurry polyethylene
process by Chevron Phillips, Innovene staged loop slurry process by
Ineos, part of the Borstar staged slurry loop and gas phase reactor
process for polyethylene by Borealis and part of Spheripol
polypropylene staged slurry (bulk) loop and gas phase process by
LyondellBasell. The high activity of the catalyst systems
hereinbefore described allow for efficient slurry polymerization to
be carried out. The productivity of the total catalyst system is
preferably equal to the productivity of the solid catalyst system.
Preferably, the productivity achieved based on the total (dry)
weight of the catalyst system in the polymerization process is at
least 1 ton polymer/kg of catalyst system. Still more preferably
the productivity of the total catalyst system is at least 2 ton
polymer/kg catalyst system, e. g. at least 3 ton polymer/kg
catalyst system. The upper limit is not critical but might be in
the order of 30 ton polymer/kg catalyst system. Advantageously, the
process typically proceeds without reactor fouling.
[0117] Slurry Reactor Parameters and Operation
[0118] The conditions for carrying out slurry polymerizations are
well established in the art. The reaction temperature is preferably
in the range 30 to 120.degree. C., e. g. 50 to 100.degree. C. The
reaction pressure will preferably be in the range 1 to 100 bar, e.
g. 10 to 70 bar. The residence time in the reactor or reactors (i.
e. in the polymerization section) is preferably in the range 0.5 to
6 hours, e. g. 1 to 4 hours. The diluent used will generally be an
aliphatic hydrocarbon having a boiling point in the range -70 to
100.degree. C. Preferred diluents include n-hexane, isobutane and
propane, especially isobutane.
[0119] Hydrogen is also preferably fed into the reactor to function
as a molecular weight regulator. Typically, and especially for
catalysts with Group 4 metallocenes with at least one
cyclopentadienyl group, the molar ratio between the feed of
hydrogen and the feed of the C.sub.2-8 alkene into the reactor
system is 1:10 000-1:500.
[0120] Preferably, the polymerization reaction is carried out as a
continuous or semi-continuous process. Thus the monomers, diluent
and hydrogen are preferably fed continuously or semi-continuously
into the reactor. Preferably, the catalyst system is also fed
continuously or semi-continuously into the reactor. Still more
preferably polymer slurry is continuously or semi-continuously
removed from the reactor. By semi-continuously is meant that
addition and/or removal is controlled so they occur at relatively
short time intervals compared to the polymer residence time in the
reactor, e.g. between 20 seconds to 2 minutes, for at least 75% (e.
g. 100%) of the duration of the polymerization.
[0121] Thus in a preferred process the catalyst system is
preferably injected into the reactor at a rate equal to its rate of
removal from the reactor. An advantage of the invention herein
described, however, is that because less catalyst system can be
used per kg of polymer produced, less catalyst system is removed
from the reactor along with polymer. The interpolymers obtained
directly from the polymerization therefore comprise less impurities
deriving from the catalyst system.
[0122] When used with a 3-substituted C.sub.4-10 alkene comonomer,
the particulate catalyst system herein described gives a very high
activity, enabling a high productivity (ton polymer/kg catalyst
system). Consequently relatively low concentrations of catalyst
system are required in the reactor. Preferably, the concentration
of catalyst system in the slurry polymerization is less than 0.3
kg/ton slurry, still more preferably less than 0.2 kg/ton slurry,
e. g. less than 0.1 kg/ton slurry. Preferably, the concentration of
catalyst system is at least 0.01 kg/ton slurry. Preferably, the
concentration of polymer present in the reactor during
polymerization is in the range 15 to 55% wt based on total slurry,
more preferably 25 to 50% wt based on total slurry. Such a
concentration can be maintained by controlling the rate of addition
of monomer, the rate of addition of diluent and catalyst system
and, to some extent, the rate of removal of polymer slurry from the
slurry reactor. For bulk polymerization of propylene, the
controlling parameters for polymer concentration are the propylene
and catalyst system feed rates.
[0123] Staged Polymerization Including a Gas Phase
[0124] The above-described slurry polymerization may be combined
with one or more further polymerizations, i. e. in a multistage
process. Thus, for example, two slurry polymerizations can be
carried out in sequence (e. g. in Mitsui, Hostalen or Innovene
slurry processes) or a slurry polymerization can be followed by a
gas phase polymerization (e. g. in Borstar or Spheripol processes).
Alternatively, a slurry polymerization may be preceded by a gas
phase polymerization.
[0125] When a polymer is produced in a multistage process, the
reactors may be in parallel or in series but arrangement in series
is preferred. If the polymer components are produced in a parallel
arrangement, the powders are preferably mixed and extruded for
homogenization.
[0126] When a polymer is produced in a sequential multistage
process, using reactors coupled in series and using different
conditions in each reactor, the polymer components produced in the
different reactors will each have their own molecular weight
distribution and weight average molecular weight. When the
molecular weight distribution curve of such a polymer is recorded,
the individual curves from these fractions are superimposed into
the molecular weight distribution curve for the total resulting
polymer product, usually yielding a curve with two or more distinct
maxima. The product of a multistage polymerization is usually a
multimodal polyalkene.
[0127] If a gas phase polymerization is additionally employed then
the conditions are preferably as follows: [0128] the temperature is
within the range of 50-130.degree. C., preferably 60-115.degree. C.
[0129] the pressure is within the range of 10-60 bar, preferably
10-40 bar [0130] hydrogen would be added for controlling the molar
mass in a manner known in the art (e. g. at a concentration of
5-1000 ppm mol) [0131] the residence time is typically 0.5 to 3
hours.
[0132] The gas used will commonly be a non-reactive gas such as
nitrogen together with monomer (e. g. ethylene) and optionally a
3-substituted C.sub.4-10 alkene comonomer. Alternatively, another
comonomer may be added with the 3-substituted C.sub.4-10 alkene
comonomer. Alternatively, no comonomer may be added. Additionally a
low boiling point hydrocarbon such as propane is preferably
added.
[0133] When no comonomer is added in the gas phase polymerization,
the polymer component from the gas phase polymerization is an
alkene homopolymer. The polymerization may be conducted in a manner
known in the art, such as in a bed fluidized by circulating gas
acting as a coolant, monomer supply and agitation agent or in a
mechanically agitated fluidized bed or in a circulating bed. The
polymer product may be recovered from gas phase reactors using
techniques conventional in the art.
[0134] Staged processes for polyethylene preferably produce a
combination of a major component A of lower molecular weight and
lower (especially preferred is zero when producing final products
of density higher than 940 g/dm.sup.3) comonomer content and one
major component B of higher molecular weight and higher comonomer
content. Component A is preferably made in a reactor A` wherein the
hydrogen level is higher and the comonomer level lower than in the
reactor B' where component B is made. If reactor A' precedes B', it
is preferred that hydrogen should be stripped off from the polymer
flow from A' to B'. If reactor B' precedes A', then preferably no
extra comonomer is added to reactor B', and it is preferred to
remove a significant part of the non converted comonomer from the
polymer flow from B' to A'. It is also preferred that the
3-substituted C.sub.4-10 alkene is used in the reactor where the
polymer with highest incorporation of comonomer is produced, and
especially preferred in all the reactors of the process where
comonomer is used.
[0135] When a two stage polymerization is utilized, the lower
molecular weight polymer component is preferably produced in the
slurry reactor as described in detail above. The higher molecular
weight component may be produced in another slurry reactor or in a
gas phase reactor. The higher molecular weight component is
typically produced using a lower hydrogen/monomer feed. The
reactors may be connected in parallel or in series, but preferably
they are connected in series. Preferably, the same catalyst system
is used in both reactors. Preferably, the catalyst system is only
fed into the first reactor and flows from this, along with polymer,
to the next reactor(s) in sequence. The higher molecular weight
component may be an interpolymer (e. g. copolymer) or homopolymer.
Preferably, it is a copolymer, and more preferably, it is a
copolymer comprising a 3-substituted C.sub.4-10 alkene as
hereinbefore described.
[0136] A prepolymerization may be employed as is well known in the
art. In a typical prepolymerization less than about 5% wt of the
total polymer is produced. A prepolymerization does not count as a
stage with regard to consideration of whether a process is a single
or multistage process.
[0137] Preferably, however, the process of the present invention is
a single stage polymerization in a slurry reactor.
[0138] Multimodal polymers may alternatively be prepared by using
two or more different single site catalysts in a single
reactor.
[0139] Alternatively, multisite catalyst systems, as described
above, may be used to prepare multimodal polymers. In this case, in
order to achieve the optimum polymer properties, especially in a
single reactor system, it is preferably for the multisite catalyst
system to have as high a ratio as possible between the
incorporation of comonomer on a more incorporating site I and on
another less incorporating site II. It has been surprisingly found
that the 3-substituted C.sub.4-10 alkene comonomer as hereinbefore
described, for numerous combinations of active sites, gives a
higher ratio compared to the corresponding reaction using
conventional comonomers like 1-butene and 1-hexene. Utilizing
3-substituted C.sub.4-10 alkene with a multisite catalyst system is
therefore especially favorable.
[0140] Multimodal polymer may therefore be obtained in a single
reactor or in a system of two or more reactors, e. g. in a staged
reactor process. Preferably, however, a single reactor process
(except optional prepolymerization reactors making less than 7% of
the total polymer) is used. Preferably, a multisite catalyst system
comprising two or more (e. g. two) metallocene active site
precursors is used.
[0141] A further possibility is to blend different interpolymers as
hereinbefore described, e. g. prior to pelletization. Blending is,
however, less preferable to the production of multimodal polymer,
e. g. by multistage polymerization or by the use of two or more
different single site catalysts in a single reactor.
[0142] Multimodal and Unimodal Polymers
[0143] Multimodal interpolymers as hereinbefore described, and
especially those wherein the higher molecular weight polymer
component A has a higher comonomer content than the lower molecular
weight component B, may in some instances possess some advantages
over unimodal interpolymers.
[0144] Compared to unimodal interpolymer, at the same density and
at the same high ease of extrusion as regards extruder screw and
die processes, a multimodal interpolymer comprising, e. g. ethylene
and a 3-substituted C.sub.4-10 alkene, may be prepared having a
higher stress crack, brittle crack hoop stress failure and/or slow
crack growth resistance. Such interpolymers are particularly useful
for moulding and pipe applications where they give improved
resistance to stress crack and slow crack propagation as well as in
film applications wherein they allow improved impact resistance and
often improved tear resistance.
[0145] Additionally, multimodal interpolymers as hereinbefore
described also have higher melt strength, equivalent to sagging
resistance, which is an advantage in extrusion of large pipes and
blow moulding of articles, especially of large pieces.
[0146] Multimodal interpolymers as hereinbefore described may also
exhibit improved sealing properties (e. g. lower minimum sealing
temperature, sealing temperature range broadness) compared to an
unimodal polymer of the same density and ease of extrusion. This is
particularly useful in the manufacture of films.
[0147] On the other hand, unimodal interpolymers as hereinbefore
described often have a lower viscosity at very low shear stress
compared to multimodal interpolymers. This is useful, for example,
in rotomoulding processes where better mechanical strength of the
product can be achieved with the same cycle time. Furthermore such
interpolymers may possess a low degree of warpage making them
advantageous for injection moulding.
[0148] Downstream Requirements and Process
[0149] When the final polymer product is obtained from a slurry
reactor, the polymer is removed therefrom and the diluent
preferably separated from it by flashing or filtration. The major
part of the diluent and unconverted comonomer is recycled back to
the polymerization reactor(s). Preferably, the polymer is then
dried (e. g. to remove residues of liquids and gases from the
reactor). Due to its relatively low content of catalyst system
residues, preferably the polymer is not subjected to a deashing
step, i. e. to washing with an alcohol, optionally mixed with a
hydrocarbon liquid, or water.
[0150] In order that the polymer can be handled without difficulty,
both within and downstream of the polymerization process, the
polymer powder from the reactor(s) should be in a free-flowing
state, preferably by having relatively large particles of high bulk
density, e. g. less than 10% wt of the polymer being smaller than
100 .mu.m size, and the loose bulk density being higher than 300
kg/m.sup.3.
[0151] Preferably, the processes from the polymerization until the
pelletization extruder outlet are carried out under an inert (e. g.
N.sub.2) gas atmosphere.
[0152] Antioxidants are preferably added (process stabilizers and
long term antioxidants) to the polymer. As antioxidant, all types
of compounds known for this purpose may be used, such as sterically
hindered or semi-hindered phenols, aromatic amines, aliphatic
sterically hindered amines, organic phosphates and
sulphur-containing compounds (e. g. thioethers).
[0153] Preferably, the antioxidants are selected from the group of
organic phosphates and sterically hindered or semi-hindered
phenols, i. e. phenols which comprise two or one bulky residue(s),
respectively, in ortho-position to the hydroxy group, and sulphur
containing compounds.
[0154] Representative examples of sterically hindered phenolic
compounds include 2,6-di-tert.-butyl-4-methyl phenol;
pentaerythrityl-tetrakis(3-(3',5'-di-tert.-butyl-4-hydroxyphenyl)-propion-
-ate; octadecyl 3-(3',5'-di-tert.-butyl-4-hydroxyphenyl)propionate;
1,3,5-trimethyl-2,4,6-tris-(3,5-di-tert.-butyl-4-hydroxyphenyl)benzene;
2,2'-thiodiethylene-bis-(3,5-di-tert.-butyl-4-hydroxyphenyl)-propionate;
calcium-(3,5-di-tert.-butyl-4-hydroxy benzyl
monoethyl-phosphonate);
1,3,5-tris(3',5'-di-tert.-butyl-4'-hydroxybenzyl)-isocyanurate;
bis-(3,3-bis-(4'-hydroxy-3'-tert.-butylphenyl)butanoic
acid)-glycolester; 4,4'-thiobis(2-tert.-butyl-5-methylphenol);
2,2'-methylene-bis(6-(1-methyl-cyclohexyl)para-cresol);
n,n'-hexamethylene bis(3,5-di-tert.
butyl-4-hydroxy-hydrocinnamamide;
2,5,7,8-tetramethyl-2-(4',8',12'-trimethyltridecyl)chroman-6-ol;
2,2'-ethylidenebis(4,6-di-tert.-butylphenol);1,1,3-tris(2-methyl-4-hydros-
y-5-tert.-butylphenyl)butane;
1,3,5-tris(4-tert.-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4-
- ,6-(1h,3h,5h)-trione;
3,9-bis(1,1-dimethyl-2-(beta-(3-tert.-butyl-4-hydroxy-5-methylphenyl)prop-
-ionyloxy)ethyl)-2,4,8,10-tetraoxaspiro(5,5)undecane;
1,6-hexanediyl-bis(3,5-bis(1,1-dimethylethyl)-4-hydroxybenzene-propanoate-
); 2,6-di-tert.-butyl-4-nonylphenol;
3,5-di-tert.-butyl-4-hydroxyhydrocinnamic acid triester with
1,3,5-tris(2-hydroxyethyl)-s-triazine-2,4,6(1h,3h,5h)-trione;
4,4'-butylidenebis(6-tert.butyl-3-methylphenol); 2,2'-methylene
bis(4-methyl-6-tert.-butylphenol);
2,2-bis(4-(2-(3,5-di-t-butyl-4-hydroxyhydrocinnamoyloxy))ethoxyphenyl))pr-
opane;
triethyleneglycole-bis-(3-tert.-butyl-4-hydroxy-5methylphenyl)propi-
onate; benzenepropanoic acid,
3,5-bis(1,1-dimethylethyl)-4-hydroxy-c.sub.13-15-branched and
linear alkyl esters; 6,6'-di-tert.-butyl-2,2'-thiodi-p-cresol;
diethyl((3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl)methyl)phosphonate;
4,6-bis(octylthiomethyl)o-cresol; benzenepropanoic acid,
3,5-bis(1,1-dimethylethyl)4-hydroxy-c.sub.7-9-branched and linear
alkyl
esters;1,1,3-tris[2-methyl-4-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyl-
oxy]-5-t-butylphenyl]butane; and a butylated reaction product of
p-cresol and dicyclopentadiene.
[0155] Among those compounds, the following phenolic-type
antioxidant compounds are especially preferred to be included:
pentaerythrityl-tetrakis(3-(3',5'-di-tert.-butyl-4-hydroxypheyl)-propiona-
te; octadecyl 3-(3',5'-di-tert.-butyl-4-hydroxyphenyl)propionate;
1,3,5-trimethyl-2,4,6-tris-(3,5-di-tert.-butyl-4-hydroxyphenyl)benzene;
1,3,5-tris(3',5'-di-tert.-butyl-4'-hydroxybenzyl)isocyanurate,
bis-(3,3-bis-(4'-hydroxy-3'-tert.-butylphenyl)butanoic
acid)-glycolester; and
3,9-bis(1,1-dimethyl-2-(beta-(3-tert.-butyl-4-hydroxy-5-methylphenyl)-
propionyloxy)ethyl)-2,4,8,10-tetraoxaspiro(5,5)undecane.
[0156] Preferred organic phosphate antioxidants contain a phosphite
moiety or a phosphonite moiety. representative examples of
preferred phosphite/phosphonite antioxidants include
tris(2,4-di-t-butylphenyl)phosphite;
tetrakis-(2,4-di-t-butylphenyl)-4,4'-biphenylen-di-phosphonite,
bis(2,4-di-t-butylphenyl)-pentaerythrityl-di-phosphite;
di-stearyl-pentaerythrityl-di-phosphite; tris-nonylphenyl
phosphite;
bis(2,6-di-t-butyl-4-methylphenyl)pentaerythrityl-di-phosphite;
2,2'-methylenebis(4,6-di-t-butylphenyl)octyl-phosphite;
1,1,3-tris(2-methyl-4-ditridecyl phosphite-5-t-butylphenyl)butane;
4,4'-butylidenebis(3-methyl-6-t-butylphenyl-di-tridecyl)phosphite;
bis(2,4-dicumylphenyl)pentaerythritol diphosphite;
bis(2-methyl-4,6-bis(1,1-dimethylethyl)phenyl)phosphorous acid
ethylester; 2,2',2''-nitrilo
triethyl-tris(3,3'5,5'-tetra-t-butyl-1,1'-biphenyl-2,2'-diyl)phosphite);
phosphorous acid, cyclic butylethyl propandiol,
2,4,6-tri-t-butylphenyl ester;
bis(2,4,6-tri-t-butylphenyl)-pentaerythrityl-di-phosphite;
2,2'-ethylidenebis(4,6-di-t-butylphenyl)fluorophosphonite,
6-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy)-2,4,8,10-tetra-tert.but-
-yldibenz(d,t)(1.3.2)dioxaphosphepin; and
tetrakis-(2,4-di-t-butyl-5-methyl-phenyl)-4,4'-biphenylen-di-phosphonite.
[0157] Among the above-mentioned compounds, the following
phosphite/phosphonite antioxidant compounds are preferred to be
included:
tetrakis-(2,4-di-t-butylphenyl)-4,4'-biphenylen-di-phosphonite;
bis(2,6-di-t-butyl-.4-methylphenyl)pentaerythrityl-di-phosphite;
di-stearyl-pentaerythrityl-di-phosphite; and
bis(2,4-dicumylphenyl)pentaerythritol diphosphite.
[0158] As antioxidant either a single compound or a mixture of
compounds may be used. Particularly preferably a sterically
hindered phenolic compound and a phosphite/phosphonite compound may
be used in combination. The sterically hindered phenolic compound
typically acts as a long term stabilizer. The phosphite/phosphonite
compound typically acts as a process stabilizer.
[0159] The skilled man can readily determine an appropriate amount
of antioxidant to include in the polymer. As discussed above,
however, the polymers produced by the process of the present
invention comprise less catalyst system residues than conventional
polymers thus it is possible to add less antioxidant thereto. Thus
a sterically hindered phenolic antioxidant may be used in an amount
of 200-1000 ppmwt, more preferably 300-800 ppmwt, e. g. 400-600
ppmwt or about 500 ppmwt. The amount of organic
phoshite/phosphonite antioxidant present in the polymer is
preferably 50-500 ppmwt, more preferably 100-350 ppmwt and most
preferably 150-200 ppmwt.
[0160] The above-mentioned antioxidants are particularly preferred
when the amount of transition metal present in the polymer is
sufficient to accelerate oxidation reactions, e. g. when the level
of transition metal in the polymer is more than 1 .mu.mol
transition metal per kg polymer, more typically more than 2 .mu.mol
transition metal per kg polymer, e. g. more than 6 .mu.mol
transition metal per kg polymer. Such levels of transition metals
may occur as the interpolymers are often prepared without a washing
(e. g. deashing) step.
[0161] Other additives (antiblock, color masterbatches,
antistatics, slip agents, fillers, UV absorbers, lubricants, acid
neutralizers and fluoroelastomer and other polymer processing
agents) may optionally be added to the polymer.
[0162] Prior to introduction into the plastic converter, the
polymer is preferably further processed to achieve less than 10% wt
of the polymer being smaller than 2 mm in average size (weight
average) and a loose bulk density of higher than 400
kg/m.sup.3.
[0163] The polymer or polymer mix is preferably extruded and
granulated into pellets. Prior to extrusion, the polymer preferably
contacts less than 1 kg/ton, still more preferably less than 0.1
kg/ton, water or alcohol. Prior to extrusion, the polymer
preferably does not contact acid.
[0164] Additives (e. g. polymer processing agents or antiblock) may
be added after pelletization of the polymer. In this case the
additives are preferably used as masterbatches and pellets mixed
therewith before being extruded or moulded into films or
articles.
[0165] Polymer Composition and Properties
[0166] The amount of C.sub.2-8 alkene (e. g. ethylene) monomer
present in the interpolymer of the invention is preferably
60-99.99% wt, still more preferably 80-99.9% wt, e. g. 90-99.5% wt.
In interpolymers wherein the largest amount of C.sub.2-8 alkene is
propylene, preferably at least 3-10% wt of ethylene is additionally
present.
[0167] The amount of 3-substituted C.sub.4-10 alkene (e. g.
3-methyl-1-butene) monomer present in the interpolymer of the
invention is preferably 0.01 to 40% wt, more preferably 0.1-20% wt,
e. g. 0.5-10% wt, more preferably less than 7% wt.
[0168] When it is stated herein that the amount of a given monomer
present in a polymer is a certain amount, it is to be understood
that the monomer is present in the polymer in the form of a repeat
unit. The skilled man can readily determine what is the repeat unit
for any given monomer.
[0169] The density of the interpolymer of the invention is
preferably in the range 835-970 kg/m.sup.3. When the C.sub.2-8
alkene is ethylene, the density is preferably in the range 880-950
kg/m.sup.3, still more preferably in the range 910-940 kg/m.sup.3,
e. g. 920-930 kg/m.sup.3.
[0170] When the C.sub.2-8 alkene is propylene, the density is
preferably in the range 880-910 kg/m.sup.3, still more preferably
in the range 885-910 kg/m.sup.3, e. g. 890-910 kg/m.sup.3. When the
C.sub.2-8 alkene is propylene, the xylene solubles of the
interpolymer is preferably in the range 0.5-30% wt, more preferably
1-10% wt, e. g. 3-8% wt.
[0171] The MFR.sub.2 of the interpolymer of the invention is
preferably in the range 0.01-1000 g/10 min. When the C.sub.2-8
alkene is ethylene, the MFR.sub.2 of the polymer is preferably in
the range 0.01-500 g/10 min, more preferably in the range 0.1-100
g/10 min, e. g. 0.5-10 g/10 min. When the C.sub.2-8 alkene is
propylene, the MFR.sub.2 of the polymer is preferably in the range
0.1-1000 g/10 min, more preferably in the range 1-150 g/10 min, e.
g. 10-50 g/10 min.
[0172] The melting temperature of the interpolymer of the invention
is preferably in the range 90-240.degree. C. When the C.sub.2-8
alkene is ethylene, the melting temperature is more preferably in
the range 100-140.degree. C., still more preferably in the range
110-130.degree. C., e.g. 115-125.degree. C. When the C.sub.2-8
alkene is propylene, the melting temperature is more preferably in
the range 120-160.degree. C., still more preferably in the range
130-155.degree. C., e. g. 135-150.degree. C.
[0173] The Mn of the interpolymer of the invention is preferably in
the range 7000-500 000 g/mol. When the C.sub.2-8 alkene is
ethylene, the Mn is more preferably in the range 9000-250 000
g/mol, still more preferably in the range 15 000-150 000 g/mol, e.
g. 25 000-70 000 g/mol. When the C.sub.2-8 alkene is propylene, the
Mn is more preferably in the range 10 000-100 000 g/mol, still more
preferably in the range 14 000-70 000 g/mol, e. g. 20 000-50 000
g/mol.
[0174] The weight average molecular weight (Mw) of the interpolymer
of the invention is preferably in the range 20 000-1000 000 g/mol.
When the C.sub.2-8 alkene is ethylene, the weight average molecular
weight is more preferably in the range 30 000-700 000 g/mol, still
more preferably in the range 50 000-150 000 g/mol, e. g. 70 000-130
000 g/mol. When the C.sub.2-8 alkene is propylene, the weight
average molecular weight is more preferably in the range 30 000-700
000 g/mol, still more preferably in the range 50 000-400 000 g/mol,
e. g. 80 000-200 000 g/mol.
[0175] The Mw/Mn of the interpolymer of the invention is preferably
in the range 1-50. When the C.sub.2-8 alkene is ethylene, the Mw/Mn
of the interpolymer is preferably in the range 1-50, more
preferably in the range 2-30, e. g. 2-5. When the C.sub.2-8 alkene
is propylene, the Mw/Mn is more preferably in the range 1-10, more
preferably in the range 2-10, e. g. 2-5. When the polymer is
multimodal, each component should have M.sub.w/M.sub.n in the range
2-5, more preferably in the range 2-4, most preferably in the range
2-3.5.
[0176] Preferably, the interpolymer of the present invention is
unimodal.
[0177] The polymer chains of the interpolymer of the present
invention may be linear in the sense that they have no measurable
long chain branching. Alternatively, they may have some degree of
long chain branching, which may be made e. g. by certain catalytic
sites, especially metallocene such as CGC metallocenes, or by
polymerization with dienes or by post reactor modification, e. g.
via radicals. If present, however, long chain branching is
preferably introduced during polymerization without adding extra
reactants, e. g. by using a mono-Cp metallocene as discussed above
or metallocenes with two Cp rings (including indenyl and fluorenyl)
and having a single bridge between the Cp rings. Long chain
branching gives useful rheological properties similar to broader
molecular weight polymers (and thereby improved processing
behavior) while in reality maintaining a relatively narrow
molecular weight distribution, e. g. as measured by GPC.
[0178] The interpolymer of the present invention is obtained with
high purity. Thus the interpolymer contains only very low amounts
of catalyst or catalyst system residues. Preferably, the amount of
total catalyst system residue in the interpolymer of the invention
is less than 4000 ppm wt, still more preferably less than 2000 ppm
wt, e. g. less than 100 ppm wt. By the total catalyst system is
meant the active site precursor, activator, carrier or other
catalyst particle construction material and any other components of
the catalyst system.
[0179] Transition metals are harmful in films in far lower
concentrations since they act as accelerators for degradation of
the polymer by oxygen and temperature, giving discoloration and
reducing or destroying mechanical properties. A particular
advantage of the process of the present invention is that it yields
polymers containing very low amounts of transition metal. Polymers
produced by the process of the invention preferably comprise less
than 100 .mu.mol transition metal per kg polymer, more preferably
less than 50 .mu.mol transition metal per kg polymer, still more
preferably less than 25 .mu.mol transition metal per kg polymer, e.
g. less than 15 .mu.mol transition metal per kg polymer.
[0180] Applications
[0181] The interpolymer of the present invention is therefore
useful in a wide range of applications, especially considering it
has not been subjected to a deashing step. It may be used, for
example, in medical applications or for the manufacture of
packaging for food wherein it is important that the amount of
impurities present in the polymer is minimized.
[0182] The interpolymer may also be used in moulding as well as in
pipe applications.
[0183] Moulding
[0184] The interpolymer of the present invention may be
advantageously used in moulding applications. It may, for example,
be used in blow moulding, injection moulding or rotomoulding.
[0185] Representative examples of blow moulded articles that may be
prepared include bottles or containers, e. g. having a volume of
200 ml to 300 liters. Preferred interpolymers for blow moulding
have a density of more than 945 g/dm.sup.3, e. g. 945-970
g/dm.sup.3. Preferred interpolymers for blow moulding have a
MFR.sub.21 of 1-40 g/10 min.
[0186] Representative examples of injection moulded articles that
may be prepared include boxes, crates, thin walled packaging,
plastic housing, buckets, toys, racks, rail pads, trash cans, caps
and closures. Preferred interpolymers for injection moulding have a
density of more than 955 g/dm.sup.3, e. g. 955-970 g/dm.sup.3.
Preferred interpolymers for injection moulding have a MFR.sub.2 of
0.5-100 g/10 min.
[0187] Representative examples of rotomoulded articles that may be
prepared include water tanks, bins, containers and small boats.
Preferred interpolymers for rotomoulding have a density of 915-950
g/dm.sup.3. Preferred interpolymers for rotomoulding have a
MFR.sub.2 of 0.5-5 g/10 min.
[0188] Pipe
[0189] The interpolymer of the present invention may be
advantageously used in pipe applications. Preferably, it is used in
HDPE pipes, e. g. according to PE80 or PE100 standards. The pipes
may be used e. g. for water and gas distribution, sewer,
wastewater, agricultural uses, slurries, chemicals etc.
[0190] Preferred interpolymers for use in pipe applications have a
density of 930-960 g/dm.sup.3, preferably 940-954 g/dm.sup.3, more
preferably 942-952 g/dm.sup.3. Preferred interpolymers for use in
pipe applications also have a MFR.sub.5 of 0.1-0.5 g/10 min, more
preferably 0.15-0.4 g/10 min. Preferred interpolymers for use in
pipe applications have a MFR.sub.21/MFR.sub.5 of 14-45, more
preferably 16-37, most preferably 18-30. Preferred interpolymers
for use in pipe applications have a comonomer content of 0.8-5% wt,
more preferably 1-3% wt . If used with added carbon black, the
density of the interpolymer with the carbon black is preferably
940-970 g/dm.sup.3, more preferably 948-966 g/dm.sup.3, still more
preferably 953-963 g/dm.sup.3.
[0191] If the interpolymer comprises of more than one component it
preferably comprises:
[0192] A. A polymer component(s) which is 25-65% wt, more
preferably 35-60% wt of the interpolymer and comprises less than 1%
wt of comonomer, more preferably less than 0.5% wt comonomer and
has a MFR.sub.2 of 50-5000 g/10 min, more preferably 100-1000 g/10
min.
[0193] B. A polymer component(s) which is 25-65% wt, more
preferably 35-60% wt of the interpolymer and comprises more than
0.5% wt of comonomer, more preferably more than 1% wt and has a
MFR.sub.2 of 50-5000 g/10 min, more preferably 100-1000 g/10
min.
[0194] Having generally described this invention, a further
understanding can be obtained by reference to certain specific
examples which are provided herein for purposes of illustration
only, and are not intended to be limiting unless otherwise
specified.
EXAMPLES
[0195] The present invention will now be described with reference
to the following non-limiting examples wherein:
[0196] FIG. 1 is a plot of activity coefficient versus polyethylene
density; and
[0197] FIG. 2 is a plot of comonomer content versus polyethylene
density.
[0198] Determination Methods
[0199] Unless otherwise stated, the following parameters were
measured on polymer samples as described in the Tables that follow
below.
[0200] MFR.sub.2, MFR.sub.5 and MFR.sub.21 were measured according
to ISO 1133 at loads of 2.16, 5.0, and 21.6 kg respectively. The
measurements were at 190.degree. C. for polyethylene interpolymers
and at 230.degree. C. for polypropylene interpolymers.
[0201] Molecular weights and molecular weight distribution, Mn, Mw
and MWD were measured by Gel Permeation Chromatography (GPC)
according to the following method: The weight average molecular
weight Mw and the molecular weight distribution (MWD=Mw/Mn wherein
Mn is the number average molecular weight and Mw is the weight
average molecular weight) is measured by a method based on ISO
16014-4:2003. A Waters 150CV plus instrument, equipped with
refractive index detector and online viscosimeter was used with
3.times. HT6E styragel columns from Waters (styrene-divinylbenzene)
and 1,2,4-trichlorobenzene (TCB, stabilized with 250 mg/L 2,6-Di
tert butyl-4-methyl-phenol) as solvent at 140.degree. C. and at a
constant flow rate of 1 mL/min. 500 .mu.l of sample solution were
injected per analysis. The column set was calibrated using
universal calibration (according to ISO 16014-2:2003) with 15
narrow molecular weight distribution polystyrene (PS) standards in
the range of 1.0 kg/mol to 12 000 kg/mol. These standards were from
Polymer Labs and had Mw/Mn from 1.02 to 1.10. Mark Houwink
constants were used for polystyrene and polyethylene
(K:9.54.times.10.sup.-5 dL/g and a: 0.725 for PS and K:
3.92.times.10.sup.-4 dL/g and a: 0.725 for PE). All samples were
prepared by dissolving 0.5-3.5 mg of polymer in 4 mL (at
140.degree. C.) of stabilized TCB (same as mobile phase) and
keeping for 3 hours at 140.degree. C. and for another 1 hour at
160.degree. C. with occasional shaking prior to sampling into the
GPC instrument.
[0202] Melting temperature was measured according to ISO 11357-1 on
Perkin Elmer DSC-7 differential scanning calorimetry. Heating
curves were taken from -10.degree. C. to 200.degree. C. at
10.degree. C/min. Hold for 10 min at 200.degree. C. Cooling curves
were taken from 200.degree. C. to -10.degree. C. a 10.degree. C.
per min. Melting temperature was taken as the peak of the endotherm
of the second heating.
[0203] Comonomer content (wt %) was determined based on Fourier
transform infrared spectroscopy (FTIR) determination calibrated
with C13-NMR.
[0204] Density of materials is measured according to ISO 1183:1987
(E), method D, with isopropanol-water as gradient liquid on pieces
from compression moulded plaques. The cooling rate of the plaques
when crystallizing the samples was 15 C/min. Conditioning time was
16 hours.
[0205] Xylene solubles were determined according to ISO-6427, annex
B1992.
[0206] The activity coefficient for the bench scale polymerization
runs is calculated by the following equation:
Activity_coefficient ( kg / ( g , bar , h ) = ( Yield_of _polymer _
( kg ) ) ( Catalyst_amount _ ( g ) ) ( Partial_pressure _of
_ethylene _ ( bar ) ) ( Polymerisation_time - ( h ) )
##EQU00001##
[0207] For continuous polymerizations, the activity coefficient is
analogous by using production rate of polymer instead of yield of
product and feed rate of catalyst system instead of amount fed
catalyst, and using the average residence time in the continuous
reactor.
Example 1
Use of 3-methyl-but-1-ene in Single Stage Polymerization
[0208] Raw Materials
[0209] The catalyst system ((n-Bu-Cp).sub.2 HfCl.sub.2 and MAO
supported on calcined silica) was prepared essentially according to
example 1 of WO 98/02246, except Hf was used as transition metal
instead of Zr and 600.degree. C. was used as calcination
(dehydration) temperature.
[0210] Ethylene: Polymerization grade
[0211] Hydrogen: Grade 6.0
[0212] 1-hexene: From Sasol. Stripped of volatiles and dried with
13.times. molecular sieve.
[0213] 1-octene: Polymerization grade (99.5%). N2 bubbled and dried
with 13.times. molecular sieve.
[0214] 3-methyl-1-butene: Produced by Evonik Oxeno. Purity
>99.7%. Dried with 13 .times. molecular sieve and stripped of
volatiles.
[0215] Isobutane: Polymerization grade
[0216] Slurry Polymerization Method
[0217] Polymerization was carried out in an 8 liter reactor fitted
with a stirrer and a temperature control system. The same comonomer
feeding system was used for all runs. The procedure consisted of
the following steps:
[0218] 1. Catalyst system was fed into the reactor.
[0219] 2. 3.8 liter isobutane was added to the reactor and stirring
started (300 rpm).
[0220] 3. The reactor was heated to a polymerization temperature of
85.degree. C.
[0221] 4. Ethylene, comonomer and hydrogen were added into the
reactor. The pressure was maintained at the required pressure by
the supply of ethylene via a pressure control valve. Hydrogen had
been previously mixed with ethylene in the ethylene supply
cylinder. Comonomer was also added continuously into the reactor,
proportional to the ethylene flow.
[0222] 5. The consumption of monomer was followed. When 1500-2000 g
polymer had been produced, the polymerization was stopped by
venting the reactor of volatiles and reducing the temperature.
[0223] 6. The polymer was further dried in a vacuum oven.
[0224] Further details of the polymerization procedure and details
of the resulting interpolymers are provided in Table 1 and in FIGS.
1 and 2.
TABLE-US-00001 TABLE 1 Run 1 2 3 4 5 POLYMERIZATION Catalyst feed g
1.89 1.65 1.56 1.64 1.66 Total pressure bar g 22.7 22.7 22.7 19.7
19.7 Hydrogen in molppm 640 640 620 620 620 ethylene feed Comonomer
type* M1B M1B M1B M1B M1B Comonomer start ml 50 104 166 25 100
Comonomer g/100 g 6 13 24 28 25 continuous ethylene addition to
feed Run time min 43 45 40 47 44 Yield g 1920 1970 1670 1760 1790
Activity g PE/(g 197 221 223 326 350 coefficient cat, h, bar)
POLYMER ANALYSES MFR.sub.2 g/10 min 1.5 1.6 1.6 1.5 1.2 Mw g/mol
105 000 95 000 95 000 105 000 105 000 Mn g/mol 45 000 43 000 41 000
47 000 50 000 Mw/Mn -- 2.3 2.3 2.4 2.2 2.1 Melting .degree. C.
126.3 122.5 121.2 117.4 118.2 temp. (DSC) Comon. wt % 1.4 2.3 3.4
6.0 5.5 content (FT-IR) Density PE kg/dm3 937 931.8 928.4 918.5 919
Run 6 7 8 9 10 POLYMERIZATION Catalyst feed g 2.14 2.18 2.36 2.38
2.34 Total pressure bar g 22.7 19.7 19.7 19.7 19.7 Hydrogen in
molppm 620 620 620 620 620 ethylene feed Comonomer type* 1-Hexene
1-Hexene 1-Hexene 1-Hexene 1-Octene Comonomer start ml 31 50 50 50
60 Comonomer g/100 g 5 7 8 10 11 continuous ethylene addition to
feed Run time min 51 69 79 68 76 Yield g 1810 1600 1800 1680 1800
Activity g PE/(g 138 152 138 148 145 coefficient cat, h, bar)
POLYMER ANALYSES MFR.sub.2 g/10 min 1.7 1.1 1.9 1.5 1.6 Mw g/mol 95
000 105 000 95 000 95 000 95 000 Mn g/mol 43 000 46 000 41 000 44
000 42 000 Mw/Mn -- 2.3 2.3 2.3 2.2 2.3 Melting .degree. C. 122.6
117.5 119.6 116.8 119.6 temp. (DSC) Comon. wt % 3.1 5.0 5.4 6.3 6.6
content (FT-IR) Density PE kg/dm3 931 922 922 919 920.8 *M1B:
3-methyl-1-butene
[0225] The results in Table 1 show that for the production of
comparable ethylene interpolymers the use of 3-methyl-1-butene in
conjunction with a supported catalyst system comprising a single
site catalyst allows a much higher catalytic activity to be
achieved than when 1-hexene or 1-octene is used as comonomer. This
can be seen, for example, by comparing the results obtained in runs
2 and 6 (comparative).
TABLE-US-00002 Run 2 Run 6 Comonomer 3-methyl but-1-ene 1-hexene
Catalyst activity coefficient 221 152 MFR.sub.2 1.6 1.7 Mw 95 000
95 000 Mn 43 000 43 000 Mw/Mn 2.3 2.3 DSC, Melting Temp. 122.5
122.6 Comon. content (FT-IR) 2.3 2.3 Density PE 931.8 931
[0226] Some of the results in Table 1 are also presented in FIGS. 1
and 2.
[0227] FIG. 1, a plot of activity coefficient versus polyethylene
density, shows that in order to produce a polyethylene of density
930 kg/m.sup.3, the polymerization using a particulate catalyst
system comprising a single site catalyst and 3-methyl-1-butene as
comonomer is about 1.5 times as efficient compared to using
1-hexene or 1-octene as comonomer. While at a density of 920
kg/m.sup.3, 3-methyl-1-butene as comonomer is about 2 times as
efficient compared to using 1-hexene or 1-octene as comonomer.
[0228] Moreover FIG. 2, a plot of comonomer content versus
polyethylene density, surprisingly shows that in order to produce a
polyethylene of a given density, about 20% less 3-methyl-1-butene
needs to be incorporated therein than 1-hexene or 1-octene. This
means that to produce one ton of polymer by a catalyst system as
herein described, using 3-methyl-1-butene versus 1-hexene or
1-octene, results in using more ethylene and less comonomer. Since
the cost per ton of comonomer is always very much higher than that
of ethylene, this means that there is a potential for significant
cost savings on monomer/comonomer by using 3-methyl-1-butene as
comonomer.
[0229] In addition, this means that the increase in catalyst system
activity observed in FIG. 1 translates directly into a need for
less catalyst system for the production of a given polyethylene
interpolymer having particular properties.
Example 2
Use of 3-methyl-but-1-ene in Staged Polymerization
[0230] Raw Materials and Methods
[0231] The same raw materials as in example 1 were used when
applicable, including the same catalyst.
[0232] Polymerization was carried out in an 8 liter reactor fitted
with a stirrer and a temperature control system. The same comonomer
feeding system was used for all runs. The procedure consisted of
the following steps:
[0233] 1. Catalyst system was fed into the reactor.
[0234] 2. 3.8 liter isobutane was added to the reactor and stirring
started (300 rpm).
[0235] 3. The reactor was heated to the desired polymerization
temperature of 85.degree. C.
[0236] 4. Ethylene, comonomer and hydrogen were added into the
reactor. The pressure was maintained at the required pressure by
the supply of ethylene via a pressure control valve. Hydrogen had
been previously mixed with ethylene in the ethylene supply
cylinder. Comonomer was also added continuously into the reactor,
proportional to the ethylene flow.
[0237] 5. The consumption of monomer was followed. When about 1200
g polymer had been produced, the reactor was vented, stirring
reduced to 30 rpm, the polymer dried with N.sub.2 at 70.degree. C.
and 40 g polymer sample removed.
[0238] 6. The temperature was adjusted to the desired
polymerization temperature. 400 ml propane was added and stirring
adjusted to 280 rpm.
[0239] 7. Ethylene, comonomer and hydrogen were added into the
reactor. The pressure was maintained at the desired pressure by
supply of ethylene via a pressure control valve. Hydrogen had been
previously mixed with ethylene in the ethylene supply cylinder.
Comonomer was also added continuously into the reactor,
proportional to the ethylene flow.
[0240] 8. The polymerization was stopped by venting the reactor of
volatiles and reducing the temperature.
[0241] 9. The polymer was further dried at 70.degree. C. in the
reactor with N.sub.2 flow. Further details of the polymerization
procedure and details of the resulting interpolymers are provided
in Table 2.
[0242] Results
TABLE-US-00003 TABLE 2 Run no 1 2 POLYMERIZATION STAGE 1--SLURRY
Catalyst feed g 2.91 1.93 Total pressure bar g 21 21 Reactor
temperature .degree. C. 85 85 Hydrogen in ethylene feed molppm 3550
3550 Comonomer type -- 1-hexene 3-methyl-1-butene Comonomer start
ml 30 50 Feed ratio comonomer/ethylene g/g 0.09 0.27 Fraction in
stage 1 wt % 50 50 Yield in stage 1 g 1190 1180 Run time min 47 31
Activity coefficient g PE/(g cat, h, bar) 245 368 MFR.sub.2 g/10
min 170 150 Density g/dm.sup.3 937 941 POLYMERIZATION STAGE 2--GAS
PHASE Total pressure bar g 21 21 Reactor temperature .degree. C. 70
70 Hydrogen in ethylene feed molppm 300 300 Comonomer type --
1-hexene 3-methyl-1-butene Comonomer start ml 30 50 Feed ratio
comonomer/ethylene g/g 0.09 0.29 Fraction in stage 2 wt % 50 50
Yield in stage 2 only g 1150 1140 Run time min 66 33 Activity
coefficient g PE/(g cat, h, bar) 169 334 TOTAL RUN POLYMER--POWDERS
Fraction made in stage 2 wt % 50 50 MFR.sub.2 g/10 min 2.1 1
Density g/dm.sup.3 924 920
[0243] The results in Table 2 show that when comparing
3-methyl-1-butene and 1-hexene in a staged process of one slurry
and one gas phase polymerization stage to produce relatively equal
products, 3-methyl-1-butene is superior on activity in the slurry
as well as in the gas phase stage. Thus multistage polymerization
can be advantageously carried out using 3-substituted C.sub.4-10
alkene, including cases where a slurry phase polymerization is
followed by a gas phase polymerization.
[0244] U.S. provisional patent application 61/146,938 filed Jan.
23, 2009, is incorporated herein by reference.
[0245] Numerous modifications and variations on the present
invention are possible in light of the above teachings. It is
therefore to be understood that within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described herein.
* * * * *